- In the past 10 years, metabolomics has become an integrative and indispensable part of the post-genomics approach to tackle questions on plant metabolism and its regulation in plants. Nonetheless, the dynamic range of the metabolic intermediates and their qualitative (chemical) diversity hampers the comprehensive analysis of the plant metabolome using one single platform. However, prompted by the increasing interest in routine analysis of the metabolic component, recent significant advances in experimental techniques, analytical technologies and tools for the elaboration of output data have been accomplished. Hence, our capability to identify an increasing number of metabolites and to integrate results from different approaches has greatly improved. Specific to the study of plant nitrogen metabolism, the introduction of metabolomics, alongside with transcriptomics, and metabolic flux analysis emphasized the complexity of the mechanisms regulating its assimilation and metabolism and the indissoluble interaction with carbon metabolism. In this chapter, we introduce the state of the art in metabolomics analytical tools and technologies as well as their employment to improve our understanding of nitrogen-carbon interaction in plants.